Chromatography is a widely used analytical technique for the chemical analysis and separation of molecules. Chromatography involves the separation of one or more analyte species from other matrix components present in a sample. A stationary phase of a chromatography column is typically selected so that there is an interaction with the analyte. Such interactions can be ionic, hydrophilic, hydrophobic, or combinations thereof. For example, the stationary phase can be derivatized with ionic moieties that ideally will bind to ionic analytes and matrix components with varying levels of affinity. A mobile phase is percolated through the stationary phase and competes with the analyte and matrix components for binding to the ionic moieties. The mobile phase is a term used to describe a liquid solvent or buffer solution that is pumped into a chromatography column inlet. During this competition, the analyte and matrix components will elute off of the stationary phase, preferably at different times, and then be subsequently detected at a detector. Examples of some typical detectors are a conductivity detector, a UV-VIS spectrophotometer, and a mass spectrometer. Over the years, chromatography has developed into a powerful analytical tool that is useful for creating a healthier, cleaner, and safer environment where complex sample mixtures can be separated and analyzed for various industries such as water quality, environmental monitoring, food analysis, pharmaceutical, and biotechnology.
In an effort to improve selectivity, a combination of two or more different mobile phase types can be inputted into the chromatography column where the proportion of mobile phase types changes with time (i.e., gradient elution). For example, a proportion of a stronger eluting mobile phase (e.g., polar organic solvent) can be increased with time to facilitate elution of analyte from the chromatography column. When using two or more different mobile phase types, uniform mixing of the mobile phases can be important for the generation of reproducible peak retention times.
A gradient elution pumping system can deliver varying proportions of mobile phase types as a function of time. In an embodiment, a proportioning pump can be used to draw upon a plurality of different type of mobile phase reservoirs. The proportioning pump can draw from one mobile phase reservoir type for a predetermined time interval and then from a different mobile phase reservoir type for another predetermined time interval. During a single piston cycle, the proportioning pump will output a solvent volume that contains a portion of both mobile phase types. This heterogeneous solvent volume includes a plug of one mobile phase type immediately adjacent to another plug of another mobile phase type. Even though the mobile phase types can be miscible with each other, the outputted heterogeneous solvent volume still requires mixing. In order to achieve reproducible and predictable chromatographic results, the adjoining slugs of mobile phase can be homogeneously mixed prior to being inputted into the separation column.
A mixer can be dynamic where it includes a moving part to homogenize the mobile phase types. However, Applicant believes that such a mechanical device is prone to mechanical failure and wear fragments of such a device may contaminate downstream fluid components possibly compromising performance.
A static mixer where there is no moving part circumvents mechanical failure issues with dynamic mixers. Applicant believes that there is a need for static mixers that have a scalable void volume so that the time resolution of the mixing can be adjusted for a particular gradient elution system. Applicant also believes that there is a need for static mixers that have a relatively fast wash through times and be configured for handling relatively high pressure.